Method and device for depositing adhesive on an alveolar surface

ABSTRACT

A glue film ( 11 ) on a cellular structure ( 10 ) in order to form a regular glue strip on the edges of the partitions of the cells of the cellular structure ( 10 ), and the glue film ( 11 ) is exposed to a source ( 24 ) that emits radiation adapted to reactivity of the glue to only heat the glue selectively. The glue thus creeps without significantly triggering polymerisation. The glue strip is formed on the ends of the partitions without supplying an air flow through the openings of the cellular structure. The portion of the part located below the source is preferably kept approximately horizontal so that the glue strip is formed under the best possible conditions.

This application claims priority based on International PatentApplication No. PCT/FR02/01426, entitled “Process and Device ForDeposition Of Glue On A Cellular Surface” by Bernard Colin et al., whichclaims priority of French Patent Application Serial No. 01 05868, filedon May 2, 2001.

TECHNICAL FIELD

The invention relates to a process for distributing glue previouslydeposited on a cellular surface of a cellular material with tubularcells, without obstructing cells opening up from this surface.

The invention also relates to a device using this process.

The process and device according to the invention are advantageouslyapplicable to the manufacture of sandwich panels comprising a cellularcore, such as a honeycomb structure with two opposite faces on which thewalls forming the outside skin of the panel are glued. These panels areused in many fields, particularly including the aeronautical and spaceindustries.

STATE OF PRIOR ART

Sandwich panels are usually assembled by gluing. In this case, one knownmethod consists of depositing an adhesive film over the surface of thetwo faces of the cellular core. The walls are then glued on the saidfaces by contact with this adhesive film. If necessary, a gluepolymerisation operation is then applied.

However, there are disadvantages with this known method. The glue thencovers the entire two surfaces of the cellular core, including hollowparts of the cells. This makes it impossible to use this method when atleast one of the walls of the panel must remain porous after the gluingphase.

Different solutions have been imagined to overcome this problem. Allthese solutions are aimed at leaving glue only at the ends of cellpartitions.

One first known technique is proposed by the MacKAY Industries Company,Inc., U.S.A. This consists of using a hot air flow to heat an adhesivefilm previously deposited on one of the faces of the cellular core. Whena certain temperature is reached, the glue becomes fluid and migratesonto the ends of the partitions of the cells to form a glue strip onthem.

This known technique has several disadvantages. Thus, it can only beused satisfactorily on a single face of the cellular core, since thecells have to be open at their opposite end. If the cells are closed,the hot air flow that heats the glue film also heats the air containedin the cells, such that the air expands and causes a back pressureopposing the mechanical action of the hot air flow. Consequently, theglue strip is not uniform and glue may be splashed inside the cells.This can sometimes result in an incomplete glue strip and a risk ofclosing off a porous wall added on onto the cellular core later, due tosubsequent flow of the glue along the partitions of the cells duringfinal polymerisation.

FIGS. 8 a, 8 b, 8 c, 8 d and 8 e in the appended drawingsdiagrammatically illustrate cases of an incomplete glue strip (FIG. 8 a)and incorrect strips (FIGS. 8 b to 8 e) that might be obtained by thisknown process. For comparison, FIGS. 9 a and 9 b show a regular anduniform glue strip that can guarantee correct assembly of a sandwichpanel in a perspective and sectional view respectively.

Another known technique is described in document U.S. Pat. No.5,944,935. In this case, glue films previously deposited on each of thefaces of the cellular core are covered by a porous screen. The assemblyis then pressed and heated. The glue films become fluid under thecombined effects of temperature and pressure, and migrate into theporous structure of the screens adjacent to the cells, while leaving aglue deposit on the ends of the partitions of the cells. The glue isthen cooled using a cooling cylinder and the screen is graduallyremoved, leaving the glue strips on the ends of the partitions of thecells.

This other known technique also has several disadvantages. Firstly, itis long and complex to implement since it includes many additionaloperations compared with other known gluing methods (placement of porousscreens, application of pressure, cooling, removal of screens, etc.).Furthermore, this technique is more expensive than other known methodssince it also needs more glue. A thicker glue film is necessary becausea large part of the glue is removed with the porous screens.Furthermore, this induces a large quantity of waste (glue and screens)which creates problems with the environment. Furthermore, as in theprevious technique, heating of the cellular core can cause deformationsof the core, particularly in the case of complex shapes. Finally, thistechnique is difficult to apply to non-plane surfaces, for exampleconcave or convex spherical shaped surfaces.

PRESENTATION OF THE INVENTION

The purpose of the invention is a process to obtain a regular anduniform glue strip adapted to the required performances, on the ends ofthe partitions of open or closed cells of a cellular surface, regardlessof the shape of the said surface, in other words equally well on asimple shaped cellular surface and on a complex shaped surface such as anon-adjusted and/or non-developable surface.

In this respect, a process is proposed to obtain a glue strip on theends of cell partitions opening up onto a surface of a cellularstructure, according to which a glue film is deposited on the saidsurface, characterized in that the glue film is then exposed to a sourceemitting radiation adapted to the glue reactivity to heat it onlyselectively, so that it can creep without significantly triggeringpolymerisation.

The expression “without significantly triggering polymerisation” coversthe case in which polymerisation is slightly triggered, to prevent theglue from flowing during subsequent gluing and to guarantee mechanicalperformances of the glued assembly. In particular, thisprepolymerisation may be envisaged when the viscosity of the glue usedis low.

This process selectively and uniquely heats the glue to a sufficientlyhigh temperature to make it creep and migrate forming a strip on theends of the partitions of the cells, and to pre-polymerise it ifnecessary (as a function of the viscosity, wetting characteristics,etc.). It may then be used indifferently on any shape of cellularsurface, even if it is a complex shaped surface.

In one preferred embodiment of the invention, the glue film is exposedto a flux output from the source for a duration and at a power adaptedto the reactivity of the glue.

In this case, the power of the source, the distance between the sourceand the cellular structure, and the relative displacement velocitybetween the source and the cellular structure are advantageouslycontrolled using a servo control sensitive to at least one temperaturemeasurement made on the said structure.

Advantageously, the glue film is exposed to the source when the surfaceof the cellular structure is facing upwards, preferably keeping thepartitions of the cells approximately vertical. This arrangement ensuresthat the glue strip is formed as uniformly as possible on each side ofthe ends of the cell partitions.

According to one preferred embodiment of the process according to theinvention, a glue film is applied in which at least one hole is formedfacing each of the cells of the cellular structure. This characteristicfacilitates triggering of creep of the glue, and consequently formationof the strips.

Preferably, the holes formed in the glue film then have an approximatelycircular cross section and their diameter is not uniform throughout thethickness of the film.

If the cells form a regular hexagonal network, the holes are thendistributed in the glue film according to a regular network with atriangular pitch.

Another purpose of the invention is a device to form glue strips on theends of cell partitions opening up onto a surface of a cellularstructure, this device being characterized in that it comprises a sourcethat may be arranged facing the said surface on which a glue film hasalready been deposited, the said source being capable of emittingradiation chosen to selectively heat the glue only, so that it creepswithout significantly triggering its polymerisation.

According to a first embodiment of the invention, the source is fixedand the support of the cellular structure can be displaced to make thesurface of the cellular structure move in front of the source at anapproximately constant spacing.

According to a second embodiment of the invention, the support is fixedand the electromagnetic source is capable of moving parallel to thesurface of the cellular structure.

According to a third embodiment of the invention, used in the case inwhich the surface of the cellular structure is not plane, the supportcan be oriented and the source can be displaced facing the said surfacealong a trajectory keeping an approximately constant separation from theface.

In the various embodiments of the invention, the source isadvantageously capable of moving along a direction approximately normalto the surface of the cellular structure. This guarantees homogeneity ofexposure to radiation emitted by the source over the entire surface ofthe cellular structure.

The upstream and downstream screens may be associated with the sourcefor a similar purpose, in order to limit dispersion of the flux emittedby the source. These screens may be reflective or non-reflective.

In order to precisely measure the temperature reached by the glue filmon the cellular structure, the support advantageously comprises at leasta smooth lateral part, in other words with no cellular structure, ontowhich a control glue film identical to the glue film placed on the saidstructure can be applied directly. Temperature measurement means arethen placed facing the said smooth lateral part.

In this case, a temperature resistant adhesive tape is advantageouslyplaced on the smooth lateral part on which the control glue film will beplaced. The adhesive tape can be removed at the end of the operation andused as a means of keeping a trace of the application conditions.

BRIEF DESCRIPTION OF THE DRAWINGS

We will now describe different embodiments of the invention asnon-limitative examples, with reference to the appended drawings,wherein;

FIG. 1 is a perspective view with a partial tear out, representing asandwich panel obtained by use of the process according to theinvention;

FIG. 2 is a side view that diagrammatically shows a first embodiment ofa device conform with the invention;

FIG. 3 is a view comparable to FIG. 2 that diagrammatically shows asecond embodiment of the invention;

FIG. 4 is a view comparable to FIGS. 2 and 3 that diagrammatically showsa third embodiment of the invention;

FIG. 5 is a view comparable to FIGS. 2 to 4, that diagrammatically showsa variant of the embodiment in FIG. 2;

FIG. 6 is a perspective view that diagrammatically illustrates thearrangement of a temperature measurement system on the device in FIG. 2;

FIG. 7 is a perspective view that shows a device comparable to thatillustrated in FIG. 5, used for the treatment of a complex shapedstructure, in more detail;

FIGS. 8 a, 8 b, 8 c, 8 d and 8 e, described above, are perspective (FIG.8 a) and sectional (FIGS. 8 b, 8 c, 8 d and 8 e) views that representdefective glue strips obtained by processes according to prior art;

FIGS. 9 a and 9 b are perspective and sectional views respectively,showing regular and uniform glue strips obtained according to theinvention; and

FIG. 10 is a top view that diagrammatically illustrates an improvementto the invention, according to which a perforated adhesive film is usedin association with a cellular structure in which, in this special case,the cells form a regular hexagonal network.

DETAILED DESCRIPTION OF SEVERAL PREFERRED EMBODIMENTS OF THE INVENTION

As illustrated diagrammatically in FIG. 1, a sandwich panel that can bemade by the process according to the invention usually comprises acellular structure 10 forming the core of the panel, and two walls 12added on by gluing each face of the structure 10.

The cellular structure 10 is in the form of a wafer that may or may notbe plane, and may have parallel or non-parallel faces, without departingfrom the scope of the invention. This structure includes a large numberof cells 14 separated from each other by partitions 16. Usually, thepartitions 16 are oriented so as to be perpendicular to the two faces ofthe structure 10 and the cells 14 pass through it from one side to theother opening up on each of the two faces. However, this arrangementmust not be considered to restrict the scope of the invention. Theinvention is also applicable to cases of a cellular structure in whichthe partitions 16 are not perpendicular to the faces of the structureand in which the cells 14 only open up at one of the said faces.

As shown diagrammatically in FIG. 1, the cellular structure 10 isusually in the form of a “honeycomb” structure, in which the cells havea hexagonal cross-section. However, the cells of the structure 10 couldhave a different cross section, for example square or rectangular,without departing from the scope of the invention.

The wall or walls 12 that are provided on the surface of at least one ofthe faces of the cellular structure 10 may be of any nature and may havea porous or non-porous structure depending on the envisaged application.In particular, each wall 12 may be composed of a thin metallic wafer ormay consist of the superposition of several layers of woven or non-wovenfibres impregnated with resin, using an arrangement well known to thoseskilled in the art.

According to the invention, each wall 12 is added onto the correspondingface of the cellular structure 10 by gluing. More precisely, the firststep is to deposit a glue film 11 over the said face which is then inthe form of a flexible sheet with zero adhesion or relatively lowadhesion at ambient temperature. Due to the process according to theinvention, this glue film 11 is heated such that the glue creeps andmigrates without significantly polymerising, onto the ends of thepartition 16 materializing the surface of the cellular structure 10. Theglue thus forms a strip 18 on the ends of the partitions 16. The wall 12is then placed on the surface of the considered face of the structure10, so that it can be glued onto it during a subsequent polymerisationstep. This polymerisation step is well known to those skilled in theart, and consequently it will not be described herein.

The process according to the invention more precisely relates to thestep for heating the glue film 11, so that the glue strip 18 is obtainedon all ends of partitions 16 materializing the corresponding face of thestructure 10.

According to this process, the glue film 11 is heated by radiation usingan adapted power source, so that the glue is then only heatedselectively. The glue is chosen in advance to satisfy the mechanical,physical, chemical characteristics, etc., required for the envisagedapplication. At least most of the energy radiated by the source isabsorbed by the glue, without being significantly absorbed by thecellular structure.

In practice, the source only heats the glue because the sourcecharacteristics are chosen as a function of the glue characteristics tosatisfy the conditions as described above. In particular, this avoidsthe need to heat the partitions 16 of the cells 14 and the air that theycontain. Furthermore, the thermal inertia is very low. Therefore, thereis almost no risk that the glue will be splashed inside the cells orthat the strip 18 is incomplete.

As an example which in no way limits the scope of the invention, asource emitting in the infrared may be used for a thermosetting epoxytype glue.

When the process according to the invention is used, the power of thesource, the distance separating it from the surface of the cellularstructure and the exposure time, are determined as a function of thereactivity of the glue, such that the temperature reached by the glue issufficient for it to creep, without significantly triggeringpolymerisation. The glue can thus creep and migrate under the effect ofcapillarity forces to form the strip 18, without significantlyincreasing the temperature of the cellular structure 10, sinceessentially the glue is heated by radiation of the source. Therefore,the exposure duration/temperature pair is defined as a function of therheological characteristics and polymerisation kinetics of the glue.

In addition to the risk of polymerisation of the glue beginning due tothe use of an excessive creep temperature, such an excessive temperaturewould also cause the glue to flow along the partitions of the cells andconsequently result in a lack of glue where it should have beendeposited. Tests carried out in advance will optimise the glue exposureparameters in each special case.

Different parameters such as the velocity of the relative displacementbetween the source and the cellular structure (in other words theexposure time of the glue film), the distance between the source and thestructure and the power of the source, will advantageously be servocontrolled in order to control conditions for the formation of gluestrips at the ends of the cells in real time.

Thus the glue temperature, for example measured using opticalpyrometers, is automatically held at a sufficient value so that the gluecreeps and migrates, but is not sufficient to begin polymerisation ofthe glue too early. The temperature may be controlled by varying thepower of the source and/or its average distance from the glue film. Theadvance velocity is controlled such that the exposure duration issufficient to enable the glue to creep and migrate in the form of astrip, but is also short enough so that the polymerisation process isnot significantly triggered.

The glue film 11 is exposed to the source while the corresponding faceof the cellular structure 10 is facing upwards, so that creep can takeplace under optimal conditions capable of guaranteeing the formation ofa uniform strip 18, in other words symmetrical or approximatelysymmetrical with respect to the planes of the partitions 16 (FIG. 9 b).Furthermore, the said structure is oriented such that the partitions 16of the cells 14 are approximately vertical at least in the part of thecellular structure 10 facing the source when the said structure is notplane. The absorption efficiency of the radiation emitted by the sourceis optimised as a result of this arrangement in which the direction ofradiation of the source is oriented normal to the surface of the part.

The process according to the invention has many advantages. Thus, sincethe cellular structure is not heated, there is no risk that it willdeform. Therefore, the glue may be deposited on structures that may havea complex shape. Furthermore, the air contained in the cells does notexpand since it is not heated. Therefore, there is no risk of the gluestrip 11 bursting and the glue splashing, even if the cells are closedon the other face of the structure. Furthermore, the absence of anydirect mechanical action of the device on the part being manufactured isa means of avoiding the creation of parasite effects such asdeformations of the part, pollution or deterioration to its surface,etc. Furthermore, the process is easy to implement and enablessignificant time savings compared with processes according to prior art.It does not lead to any waste and only uses the strictly necessaryquantity of glue. Finally, the process according to the invention may beused in sequence on the two faces of a cellular structure.

Different embodiments of devices designed to implement the process thathas just been described will now be briefly presented, with reference toFIGS. 2 to 7 in sequence.

FIG. 2 diagrammatically shows a first embodiment of a device conformwith the invention. This device comprises a support 20 with a shape anddimensions adapted to the cellular structure 10, in which the ends ofthe walls of the cells are to be covered with glue strips. The case of aplane structure is illustrated, to make the description simpler. As willbe seen later, this embodiment is not limited to this type of cellularstructure and may also be used in the case of non-plane structures.

The support 20 is provided with drive and guidance means,diagrammatically illustrated in 22 in FIG. 2. These drive and guidancemeans 22 are used to displace the support 20 and the structure 10 thatit supports along a trajectory, which in this case is approximatelystraight and horizontal (arrow F1). In the case of a non-plane part,this trajectory may be significantly different as will be understoodlater.

The device diagrammatically illustrated in FIG. 2 also comprises asource 24. As will be seen in more detail later, the source 24 comprisesthe source itself, which for example is in the form of one or severalemitting tubes placed end to end, and one or several reflectorsdirecting radiation in the required direction.

In one variant embodiment, the distance and orientation of each tubewith respect to the cellular structure may be adjusted independently ofthe distance and orientation of the other tubes, such that the sourceconsidered as a whole is then in non-linear form. For example, thisarrangement is particularly advantageous in the case of sphericalcellular structures. The source itself may also be deformable or have ashape adapted to the shape of the part.

The source 24 is installed in a fixed manner above the support 20 and isoriented vertically downwards, so that it can emit radiation S with thecharacteristics defined above towards the cellular structure 10 placedon the support 20.

When the device diagrammatically illustrated in FIG. 2 is used, thestructure 10 is coated with a glue film 11 and it moves under the source24 by activating the drive and guidance means 22. The arrangement ofthese means is such that the spacing between the source 24 and thefacing part of the structure 10 remains approximately constant and thatthe radiation S emitted by the source is always approximately normal tothe said part. Servo control of the advance velocity of the structure 10in front of the source 24, the power of the source and the distancebetween the source 24 and the structure 10, optimise operation to obtainthe required temperature for creep of the glue. As already mentioned,exposure of glue to radiation from the source must be adapted to thereactive properties of the glue. In particular, it may be regulated by aservo control system or in relation to prior learning.

Since only the glue is heated by absorption of the emitted energy, thethermal inertia is very low and the structure on which the glue strip isformed very quickly returns to ambient temperature. If applicable, acooling system (not shown) may also be provided on the output side ofthe part of the cellular structure 10 facing the source 24. For example,this cooling system is then of the ventilation or suction type and maybe equipped with screens to direct the effect of ventilation towards thestructure.

In one variant of this first embodiment (not shown) that will be usedfor making small parts, the entire surface of the glue film placed onthe cellular structure 10 is heated by the source 24, without it beingnecessary to move this structure. The device can then include a support20 that is also fixed.

In a second embodiment of the device according to the inventionillustrated diagrammatically in FIG. 3, the support 20 supporting thecellular structure 10 is fixed. This embodiment essentially concerns thecase in which the surface of the cellular structure 10 facing the source24 is plane, or approximately plane. The source 24 then moves above thestructure 10 along a trajectory such that the spacing between the sourceand the said structure remains approximately constant. The upper face ofthe structure 10 in this case is approximately plane and horizontal,which means that the trajectory followed by the source 24 is straightand horizontal (arrow F2).

FIG. 4 diagrammatically shows a third embodiment of the device accordingto the invention. This embodiment is an extension of the previousembodiment, in the case in which the top face of the cellular structure10 is not plane.

As in the embodiment that has just been described with reference to FIG.3, the source 24 moves along a straight and horizontal trajectory (arrowF2) above the top face of the structure 10. However, instead of beingfixed, the support 20 on which it is installed comprises means oforientation, diagrammatically illustrated in the form of jacks 26 inFIG. 4. These orientation means keep the part of the top face of thestructure 10 located facing the source 24 approximately horizontal andat an approximately constant distance from the source 24. Theorientation means 26 may be any shape useful to obtain the requiredresult. Advantageously, they are used under the control of a servocontrol system (not shown) sensitive to signals output by sensors makingmeasurements such as temperature measurements on the cellular structure.

FIG. 5 diagrammatically shows a variant of the first embodiment of theinvention described above with reference to FIG. 2. However, note thatthis variant is also applicable to the two other embodiments that havejust been described with reference to FIGS. 3 and 4.

The variant embodiment in FIG. 5 is a means of correcting disadvantagesdue to the fact that in practice, the source 24 is neither perfectlypoint, or at the focus of a perfectly parabolic reflector. Consequently,the radiation beam emitted by the source is not perfectly parallel andhomogenous. Therefore, there are two zones 32 and 34 of diffuse andattenuated radiation on the upstream and downstream sides of the zone30, in which the glue is exposed but to a lesser extent than in zone 30.Therefore, if the distance between the source and the top face of thecellular structure is not approximately constant over the entire surfaceof the structure, the absorbed energy quantity and consequently thetemperature will not be homogenous over the entire surface.

For some applications, this phenomenon does not jeopardise smoothoperation of the process. The devices described above with references toFIGS. 2 to 4 can then be used without modification.

On the other hand, in some applications, radiation dispersion disturbssmooth operation of the process. As shown in the form of jacks 28 onFIG. 5, means can then be inserted between the source 24 and the fixedframe of the device, so that the distance separating the source 24 fromthe surface facing the cellular structure 10 can be varied at will. Aservo control then moves the source 24 vertically, so as to keep theabove mentioned distance approximately constant. In particular, thisservo control may be controlled in response to signals output bydistance sensors (not shown) carried by the source and/or temperaturesensors placed close to the source. This guarantees uniformity ofexposure over the entire surface of the part to be treated.

In another variant embodiment shown in chain dotted lines in FIG. 5, the“parasite” exposure areas 32 and 34 are reduced by adding upstream 36and downstream 38 screens to the source 24. These screens may or may notbe reflecting and may or may not be parallel to the radiation beamemitted by the source, or they may be oriented obliquely with therespect to this beam, and limit dispersion of the flux. They are locatedat a suitable distance from the structure 10.

FIG. 6 diagrammatically shows an optional advantageous improvement tothe device according to the invention. In the case in FIG. 6, thisimprovement is applied to the first embodiment described above withreference to FIG. 2. However, this improvement may be used indifferentlyin all embodiments and variants of the invention.

As shown in FIG. 6, the support 20 on which the cellular structure 10 isinstalled then also includes at least one side part 40 which is smoothand on which a control glue film 42 is placed identical to the glue film11 placed on the top face of the structure 10. A side part 40 is thenarranged along at least one of the side edges of the cellular structure,so as to extend over the entire length of the structure parallel to thedirection of relative displacement between the support 20 and the source24 (in FIG. 6, this direction corresponds to displacement of the support20 and is illustrated by the arrow F1).

The face of each side part 40 on which the control glue film 42 isplaced faces towards the source 42. Furthermore, this face is smooth andis located at approximately the same level as the top face of thecellular structure 10. Each control glue film 42 is thus scanned by theradiation emitted by the source 24 under the same conditions as the gluefilm 11 placed on the structure 10. Therefore, the temperature of thecontrol glue film 42 is representative of the temperature obtained onthe glue film 11 covering the cellular structure.

As also illustrated in FIG. 6, temperature measurement means, forexample such as at least one optical pyrometer 44, are installed closeto the source 24. The optical pyrometer 44 measures the temperatureobtained on the contact free control glue film 42. Since the side part40 is solid, the temperature of the control glue film 42 may be measuredprecisely and under good conditions, which would not be the case if themeasurement was made directly on the glue film 11 placed on thestructure 10, due to the holes that are formed in this film due tocreep.

The temperature information thus obtained may be used for differentpurposes. One first possible use is for monitoring, recording andprinting the temperature cycle applied to the part (traceability). Oneother possible use would be to regulate the temperature of the glue filmby varying the power of the flux emitted by the source. Finally, thetemperature information could be used to regulate the temperature byvarying at least one of the magnitudes consisting of the velocity ofrelative displacement between the support 20 and the source 24, and thedistance between the source and the part.

Advantageously, an adhesive tape resistant to the temperature applied tothe glue may be inserted between the lateral part 40 and the controlglue film 42. This adhesive tape then makes it easier to remove thecontrol glue film from the side part 40 after its exposure. At leastpart of the adhesive tape covered with glue can then be kept to keep atrace of part manufacturing conditions.

FIG. 7 shows an example of an industrial embodiment of the deviceaccording to the invention, in more detail. More precisely, this examplecombines embodiments and variants described above with reference toFIGS. 2, 4 and 5, in the case in which the manufactured part has anon-developable and non-adjusted cellular surface.

FIG. 7 shows the support 20 on which the cellular structure 10 is fixedby shims 46 and conventional clamping means (not shown). The (optional)shims 46 are used to install different shaped structures 10 on a singlesupport 20.

The support 20 is itself supported by a mobile frame 21, throughorientation means illustrated diagrammatically in the form of jacks 26.The use of these orientation means is a means of continuouslymaintaining the portion of the upper face of the structure 10 exposed toradiation from source 24 in an approximately horizontal orientation atan approximately constant distance from the source 24.

FIG. 7 also shows drive and guidance means 22. In this case, these meanscomprise two rails 48 fixed on the lower face of the mobile frame 21,wheels 50 supported by the fixed frame (not shown) of the device andcooperating with the rails 48, a drive gear 52 engaged on a toothedwheel 54 formed on one of the rails 48, and a motor (not shown) to drivethe gear 52.

FIG. 7 also shows the source 24. This source comprises one or severaltubes 56 forming the actual source, a parabolic reflector 58 thatdirects radiation emitted by tube 56 towards the top face of thestructure 10, and the upstream 36 and downstream 38 screens as describedpreviously with reference to FIG. 5.

The source 24 is connected to a mobile wafer 25 by two jacks 28. Themobile wafer 25 itself is installed on a moving carriage 27 through amechanism 29 enabling vertical displacement (arrow F3) and rotation(arrow F4) of the said wafer about a vertical axis. Finally, the movingcarriage 27 is installed on the fixed frame of the device so that it canmove along a translation direction illustrated by the arrow 5 in FIG. 7.

The vertical displacement (arrow F3) of the wafer 25 is used to adjustthe distance that separates the source 24 from the surface of thestructure 10. Use of the jacks 28 maintains an approximately constantmean distance between the source 24 and the top face of the cellularstructure 10, when the said face is not plane. The rotation (arrow F4)of wafer 25 is used to orient the source 24 along the generating linesof the cellular structure, when the cellular structure has a complexshape. Finally, translation of the carriage 27 along the direction ofthe arrow F5 is a means of moving the source 24 over the entire surfaceof the part.

In the arrangement that has just been described, the drive and guidancemeans 22 are used to displace the cellular structure 10 coated with aglue film under the source 24 (arrow F6) so as to gradually increase thetemperature of the assembly thus formed. The presence of the jacks 26 isa means of presenting the part of the said assembly located under theactive area of the source 24, in an approximately horizontal position.Thus, the partitions of the cells are in an approximately verticalposition when the glue film that covers them is heated by the absorptionof radiation emitted by the source.

The device shown in FIG. 7 also comprises two smooth side parts 40 ofthe support 20, conform with the improvement described above withreference to FIG. 6, on which a control glue film 42 is deposited,together with two temperature measurement means such as opticalpyrometers 44 fixed to the source 24 and oriented towards each of theside parts 40 respectively.

A non-perforated glue film 11 is used in the different embodimentsdescribed.

On the other hand, a perforated glue film 11 is used in an advantageousimprovement to the invention. This embodiment is diagrammaticallyillustrated in FIG. 10 in the special case of a cellular structure 10 inwhich the cells 40 form a regular hexagonal network.

More precisely, the glue film 11 is perforated in this case by at leastone hole 11 a facing each of the cells 40 of the cellular structure 10.The holes 11 a are intended to facilitate migration of glue towards theends of the partitions 16 of the cells 14.

However, the number, arrangement and dimensions of holes 11 a aredetermined so as to facilitate initiation of creep of the glue, whilekeeping a sufficient quantity of glue in each of the cells 14 to makethe strips 18 (FIG. 1). When the size of the holes 11 a is increased,the quantity of glue contained in the glue film becomes smaller. Inpractice, good results are obtained if the average diameter of the holes11 a is approximately equal to 1 mm, but other dimensions may besuitable.

In practice, the shapes of the holes 11 a are not cylindrical andprismatic, to facilitate migration of glue from the different holestowards the ends of the partitions of the cells when the film is heated.In particular, they are usually circular, but their diameters are notuniform over the thickness of the glue film. As a non-restrictiveexample, the holes 11 a may in particular be tapered. The expression“average diameter” used above takes account of the fact that the holes11 a preferably have a shape other than a cylinder with the circularcross-section.

When the cellular structure 10 has an approximately plane surface to beglued and cells 14 in line and arranged according to a regular network,it is possible to be sure that there is at least one hole 11 a facingeach of the cells 14 using a glue film 11 through which holes 11 a areperforated arranged according to a regular network, for which thespacing pitch corresponds to the pitch of the cells 14 along the twodirections of the plane surface to be glued.

FIG. 10 illustrates this arrangement, in the special case of a cellularstructure 10 in which the cells 14 are arranged according to a regularhexagonal network. In this case, the holes 11 a are arranged accordingto a regular triangular shaped network, in which the pitch is equal tothe pitch of the network formed by the cells 14.

In many cases, the cellular structure is flexible and deformable.Furthermore, some parts to be made are not plane. The consequence of allthese arrangements is that the cells 14 are not perfectly aligned. Inthis case, the use of a glue film like that described in the previoussection is not sufficient to guarantee the presence of a hole 11 afacing each of the cells 14 of the structure.

In order to satisfy the above mentioned contradictory requirements, aglue film 11 is then used in which the holes are arranged such that formost of the cells, the number of holes facing them is less than or equalto 3 and equal to at least 1. If there are too many holes correspondingto a single cell there is a risk that the glue will migrate irregularlyaround the perimeter of the end of this cell, particularly if the holeswere located close to the ends of the partitions of this cell.

The glue migrates more homogenously if the hole(s) is or are locatedclose to the centre of the end of the cell considered. By limiting thenumber of holes facing each cell to approximately three, gooddistribution of the glue and consequently good subsequent gluing of thewall on the cellular structure, is achieved.

When several holes (for example 2 or 3) correspond to the same end of acell, glue threads can remain in the said end after the creep andmigration operation of the glue. However, this is not a problem since inmost cases, these threads fluidise and break, and glue then migratestowards the edges of the cells during the polymerisation stepcorresponding to gluing the partition onto the cellular structure.

Many tests carried out for the purposes of this improvement have definedan optimum arrangement of the holes 11 a, even for the case of adeformed or curved structure. These tests have been carried out onhoneycomb structures made by “Eurocomposite” or “Hexcel”, comprisingapproximately hexagonal cells with dimensions such that the diameter ofthe inscribed circle in each of the cells is equal to approximately 9.5mm (⅜ inches). The glue film used was of the thermosetting type made by“3M”, reference AF191.U.

The optimum arrangement of the holes 11 a formed due to these tests isillustrated in FIG. 10. Thus, the holes 11 a are arranged in twodirections with an angle of 60° between them, in other words along aregular network with a triangular shaped pitch.

In the estimated example considered in the tests, the holes 11 a have aspacing with a pitch Px equal to approximately 7 mm along a firstdirection. The spacing of the holes 11 a along the second direction issuch that the projection Py of the pitch separating them onto astraight-line perpendicular to the first direction is equal toapproximately 4.5 mm. The result obtained with this range issatisfactory since fewer than three cells remain blocked by the gluefilm on a panel larger than 1 square meter.

For a cellular structure in which the cell sizes are different, a gluefilm perforated with holes arranged in a similar manner will be used, byapplying a proportionality factor to the values of the pitch Px and thedistance Py given in the previous section.

1. Process to obtain a glue strip on the ends of the partitions of cellsopening up onto the surface of a cellular structure, comprising:applying a glue film on said surface; and exposing the glue film to asource emitting radiation adapted to the reactivity of the glue to onlyheat the glue selectively so that the glue creeps without significantlytriggering its polymerization, wherein the glue strip is formed on theends of the partitions without bursting the glue film.
 2. Processaccording to claim 1, wherein the glue film is exposed to the source fora duration and at a power adapted to the reactive properties of theglue.
 3. Process according to claim 2, further comprising: controllingthe power of the source, the distance between the source and thecellular structure, and the relative displacement velocity between thesource and the cellular structure using a servo control sensitive to atleast one temperature measurement made on the said structure.
 4. Processaccording to claim 1, wherein the glue film is exposed to the sourcewhile the surface of the cellular structure is facing upwards. 5.Process according to claim 1, wherein the glue film is exposed to thesource while keeping the partitions of the cells approximately vertical.6. Process according to claim 1, wherein a glue film is used in which atleast one hole is perforated facing each of the cells of the cellularstructure.
 7. Process according to claim 6, wherein a glue film is usedin which approximately circular holes are formed, with a non-uniformdiameter over the thickness of the said film.
 8. Process according toclaim 6, wherein the said cells forming a regular hexagonal network, anda glue film is used in which holes are formed distributed along aregular network with a triangular shaped pitch.
 9. Device to obtain theformation of glue strips on the ends of the partitions of cells openingonto the surface of a cellular structure, said device comprising asource adapted to be placed facing said surface, on which a glue filmhas been deposited in advance, said source being capable of emittingradiation chosen to heat the glue only selectively, so that the gluecreeps without significantly triggering its polymerization, wherein saiddevice is adapted to form the glue strip on the ends of the partitionswithout bursting the glue film.
 10. Device according to claim 9, furthercomprising a support adapted to place the cellular structure thereonsaid structure being arranged such that the said surface is facingupwards.
 11. Device according to claim 9, wherein said support isadapted to arrange the structure such that the partitions of the cellsare approximately vertical.
 12. Device according to claim 9, wherein thesource is fixed, and the support of the cellular structure is adapted tomove to make said surface move in front of the source with anapproximately constant spacing.
 13. Device according to claim 9, whereinthe support is fixed and the source is capable of moving parallel to thesaid surface of the cellular structure.
 14. Device according to claim10, applicable when said surface is not plane, wherein the support isadapted to be rotated, and the source is adapted to be displaced facingsaid surface among the trajectory and with an approximately constantspacing therefrom.
 15. Device according to claim 9, in which the sourceis capable of moving along a direction approximately normal to saidsurface.
 16. Device according to claim 12, wherein upstream anddownstream screens are associated with the source in order to limitdispersion of flux emitted by the source.
 17. Device according to claim10, wherein the support comprises at least one smooth side part withoutany cellular structure, on which a control glue film is adapted to beapplied identical to the glue film placed on said structure, andtemperature measurement means placed facing said smooth lateral part.18. Device according to claim 17, wherein an adhesive tape resistant totemperature is placed on the smooth side part, on which the control gluefilm is to be applied.